The present invention generally relates to radio communications and, more particularly, to base station antennas for cellular communications systems.
Cellular communications systems are well known in the art. In a cellular communications system, a geographic area is divided into a series of regions that are referred to as “cells” which are served by respective base stations. The base station may include one or more base station antennas that are configured to provide two-way radio frequency (“RF”) communications with mobile subscribers that are within the cell served by the base station. In many cases, each base station is divided into “sectors.” In perhaps the most common configuration, a hexagonally shaped cell is divided into three 120° sectors, and each sector is served by one or more base station antennas that have an azimuth Half Power Beamwidth (HPBW) of approximately 65°. Typically, the base station antennas are mounted on a tower or other raised structure, with the radiation patterns (also referred to herein as “antenna beams”) that are generated by the base station antennas directed outwardly. Base station antennas are often implemented as linear or planar phased arrays of radiating elements.
In order to accommodate the ever-increasing volume of cellular communications, cellular operators have added cellular service in a variety of new frequency bands. While in some cases it is possible to use linear arrays of so-called “wide-band” or “ultra wide-band” radiating elements to provide service in multiple frequency bands, in other cases it is necessary to use different linear arrays (or planar arrays) of radiating elements to support service in the different frequency bands. In the early years of cellular communications, each linear array was typically implemented as a separate base station antenna.
As the number of frequency bands has proliferated, and increased sectorization has become more common (e.g., dividing a cell into six, nine or even twelve sectors), the number of base station antennas deployed at a typical base station has increased significantly. However, due to, for example, local zoning ordinances and/or weight and wind loading constraints for the antenna towers, there is often a limit as to the number of base station antennas that can be deployed at a given base station. In order to increase capacity without further increasing the number of base station antennas, so-called multi-band base station antennas have been introduced in recent years in which multiple linear arrays of radiating elements are included in a single antenna. One very common multi-band base station antenna design is the RVV antenna, which includes one linear array of “low-band” radiating elements that are used to provide service in some or all of the 694-960 MHz frequency band (which is often referred to as the “R-band”) and two linear arrays of “high-band” radiating elements that are used to provide service in some or all of the 1695-2690 MHz frequency band (which is often referred to as the “V-band”). These linear arrays are mounted in side-by-side fashion.
There is also significant interest in RRVV base station antennas, which refer to base station antennas having two linear arrays of low-band radiating elements and two (or four) linear arrays of high-band radiating elements. RRVV antennas are used in a variety of applications including 4×4 multi-input-multi-output (“MIMO”) applications or as multi-band antennas having two different low-bands (e.g., a 700 MHz low-band linear array and an 800 MHz low-band linear array) and two different high bands (e.g., an 1800 MHz high-band linear array and a 2100 MHz high-band linear array). RRVV antennas, however, are challenging to implement in a commercially acceptable manner because achieving a 65° azimuth HPBW antenna beam in the low-band typically requires low-band radiating elements that are at least 200 mm wide. When two low-band arrays are placed side-by-side, with high-band linear arrays arranged therebetween, this results in a base station antenna having a width of perhaps 600-760 mm. Such a large antenna may have very high wind loading, may be very heavy, and/or may be expensive to manufacture. Operators would prefer RRVV base station antennas having widths in the 300-380 mm range which is a typical width for state-of-the-art base station antennas.